In connection with hot melt adhesive dispensing systems, failures can generally occur within two different categories, that is, mechanical failures due to wear, or electrical failures due to electrical malfunctions. More particularly, in connection with the different types of electrical failures that can be experienced, electrical failures can occur, such as, for example, either within the heater circuit which is used to maintain the hot melt adhesive material, that is flowing through the hot melt adhesive hose assembly, at a predetermined temperature level, or within the temperature sensor which is operatively or thermally associated with the hot melt adhesive hose assembly in order to effectively detect the temperature level of the hot melt adhesive material, which is flowing through the hot melt adhesive hose assembly, and which effectively controls the heater circuit, through means of the adhesive supply unit (ASU) and its temperature controller, so as to ensure that the desired temperature level of the hot melt adhesive material, which is flowing through the hot melt adhesive hose assembly, is in fact maintained. Maintenance of the proper or desired temperature level of the hot melt adhesive material, which is flowing through the hot melt adhesive hose assembly, is therefore of course critical in order to ensure that the hot melt adhesive material will have the proper viscosity characteristics so as to be properly dispensed and therefore provide the desired adhesive properties once the hot melt adhesive material is in fact deposited onto a particular substrate. In either case, that is, whether a failure is experienced in connection with the heater circuit, or in connection with the temperature sensor, such failures typically cause the hot melt adhesive dispensing production line to be shut down for extended periods of time, in order to implement the repair or replacement of the failed components, whereby valuable production time is lost.
A hot melt adhesive dispensing apparatus employing redundant temperature sensing devices is disclosed within United States Patent Application Publication 2005/0092736 which was published on May 5, 2005 in the name of Raterman et al. More particularly, as can be appreciated from FIG. 1, which substantially corresponds to FIG. 1 of the aforenoted patent publication, the adhesive dispensing apparatus of Raterman et al. is generally indicated by the reference character 10 and is seen to comprise an adhesive dispensing gun 20 for depositing adhesive material 22 onto a substrate 24. The adhesive dispensing gun 20 is mounted upon a manifold 18, and a supply tank or adhesive supply unit (ASU) 16, containing a supply of the adhesive material 22, is fluidically connected to the manifold 18 by means of a hose assembly 12 and a pump 14, with an inlet end 42 of the hose assembly 12 being fixedly connected to the pump 14 while an outlet end 44 of the hose assembly 12 is fixedly connected to the manifold 18. The hose assembly 12 is also provided with a wire harness 28 which is connected to a controller 32, through means of an electrical connector 80, which is mounted upon the supply tank or adhesive supply unit (ASU) 16, and the supply tank or adhesive supply unit (ASU) 16 also includes a heater 26 which is selectively controlled so as to maintain the adhesive material 22, disposed within the supply tank or adhesive supply unit (ASU) 16, within a predetermined temperature range.
The hose assembly 12 further comprises a heating element and a pair of temperature sensing devices, not illustrated within FIG. 1 but fully disclosed within the aforenoted patent publication to Raterman et al., wherein the pair of temperature sensing devices sense the temperature of the adhesive material flowing through the hose assembly 12, and wherein further, the pair of temperature sensing devices are alternatively electrically connected to the controller 32 so as to in fact monitor the temperature of the adhesive material 22 flowing through the hose assembly 12. The controller 32 monitors the temperature from one or both of the two temperature sensing devices and controls the operation of the heating element, based upon the readings from the particular one or both of the two temperature sensing devices so as to maintain the hot melt adhesive material at a desired temperature level. If one of the two temperature sensing devices is found to be malfunctioning or failing, then that particular one of the two temperature sensing devices is deactivated and the other one of the two temperature sensing devices is activated or remains active so as to function within the heater control system. The switch-over between the two temperature sensing devices may be either accomplished manually, such as, for example, by hard wiring the temperature sensing devices to the controller input, or automatically through means of a suitable relay or other control operation or circuit incorporated within the controller 32.
While the hot melt adhesive dispensing apparatus employing the redundant temperature sensing devices, as disclosed within the aforenoted patent application publication to Raterman et al., is operationally satisfactory, several operational drawbacks of the apparatus are also apparent from the disclosure. For example, it is initially noted that while redundant temperature sensing devices are disclosed, there is no disclosure of redundant heating elements. This is critically important in that, as has been noted hereinbefore, electrical failures can occur within the heater circuit which is used to maintain the hot melt adhesive material, that is flowing through the hot melt adhesive hose assembly, at a predetermined temperature level, as well as within the temperature sensor which detects the temperature level of the hot melt adhesive material that is flowing through the hot melt adhesive hose assembly. Furthermore, and just as importantly, if not more importantly, as has also been noted hereinbefore, the redundant temperature sensing devices of the Raterman et al. apparatus or system are intimately connected to the temperature controller 32 that forms an integral part of the adhesive supply unit (ASU) 16. Accordingly, the hose assembly 12 is intimately dependent upon, and can only be used in conjunction with, the particular temperature controller 32 and the particular adhesive supply unit (ASU) 16. Viewed from a slightly different perspective or point of view, the hose assembly 12 of Raterman et al. does not comprise a stand-alone, self-contained, or independent operative component that can readily be used in conjunction with any adhesive supply unit (ASU), or viewed in a still similar manner, the hose assembly 12 of Raterman et al. cannot be disconnected from a particular adhesive supply unit (ASU) and readily operatively connected to another adhesive supply unit (ASU).
A need therefore exists in the art for a new and improved redundant control circuit, for use in conjunction with a hot melt adhesive hose assembly, wherein redundant electrical components could effectively be incorporated such that if a failure occurs within a particular electrical component, the failed electrical component could effectively be removed from its operative or functional disposition within the electrical circuitry, and the other electrical component could effectively be operatively or functionally incorporated into the electrical circuitry. In this manner, the hot melt adhesive dispensing production line would not need to be shut down for extended periods of time, in order to implement the replacement of the failed hot melt adhesive hose assembly, whereby valuable production time would not be lost. In addition, a need exists in the art for a new and improved redundant control circuit, for use in conjunction with hot melt adhesive hose assembly, wherein the hot melt adhesive hose assembly, having the heater circuits, the temperature sensors, and the switching mechanisms incorporated therein, effectively comprises a stand-alone, self-contained, or independent operative component which can be utilized in conjunction with any adhesive supply unit (ASU) and its temperature controller.